1. Field of Art
The present invention relates to a method of frame interpolation and an apparatus using the method of frame interpolation, for efficiently interpolating frames between successive frames of a reproduced moving-picture signal to increase the number of frames to be displayed per unit of time in reproduction of a moving-picture signal.
2. Related Art
In general, frame interpolation efficiently interpolates an additional frame between frames in a moving-picture signal carrying a plurality of frames, to increase the number of frames to be displayed per unit of time.
A recent frame interpolation technique is to produce a frame to be interpolated based on motion vectors obtained by block matching, one of fundamental technique in motion estimation.
Block matching is to detect motion vectors from a block in an image of a reference frame, the block having the highest correlation with small blocks of a base frame.
Such a frame interpolation technique is disclosed, for example, in Japanese Patent Laid-Open Publication 2000-224593.
The publication discloses intra-block area division based on block matching to aim at further accurate frame interpolation.
The known motion-compensated frame interpolation techniques perform motion compensation to image data pointed by a fixed terminal of a motion vector with respect to an initial point of the motion vector. The location of the initial point is, however, different from its original location due to motion-vector operations in interpolation. This causes a gap or superimposition in a frame to be interpolated.
Such a disadvantage is overcome by a technique disclosed in the Japanese Patent No. 2528103.
Disclosed in this patent is frame interpolation based on correlation between an anterior first frame and a posterior second frame. The correlation is geometrically found with a specific block of a frame to be interpolated as the center between the first and the second frame.
This frame interpolation technique requires no operations after obtaining motion vectors, different from the several known techniques described above, thus directly producing frames to be interpolated.
In addition, imaginary square grids on each frame to be interpolated in this frame interpolation technique do not cause a gap or superimposition in the frame to be interpolated, which otherwise occur like the above technique.
Nevertheless, this frame interpolation technique could assign an error motion vector in a still background, different from a motion vector to be assigned, due to relatively not so high correlation between objects in a first frame and a second frame.
This erroneous motion-vector assignment results in displaying the background on an image area on which the object should be displayed.
As discussed, one known motion-compensated frame interpolation technique is disadvantageous in causing a gap or superimposition in a frame to be interpolated.
The other known interpolation technique solving this problem is still disadvantageous in displaying a background on an image area on which an object should be displayed.
The known interpolation techniques therefore have difficulty in producing high-quality frames to be interpolated.